1. Technical Field
The present invention relates generally to switches, and more particularly to a switch which is energy efficient.
2. Description of Related Art
Between a power source and a loading, there is typically a switch installed to allow or disallow electricity to flow through. Conventionally, a switch may adopt a silicon controlled rectifier (SCR) for unidirectional conduction, or a triode for alternating current (TRIAC) for bidirectional conduction. Take SCR for example, the electricity provided by the power source is allowed to flow to the loading when the SCR is conducted. Though, after the SCR starts conducting current, the current consumed by the loading has to be maintained higher than the holding current of the SCR, otherwise the SCR becomes nonconducting, and the electricity is then cut off as a result.
SCRs can operate normally if applied to conventional illumination devices which use a tungsten filament to emit light, because the current consumed by a tungsten filament is always higher than the holding current of a SCR while illuminating. But since light-emitting diode (LED) consumes much less current than tungsten filament, which is also much less than the holding current of a SCR, LED illumination devices are usually provided with a pseudo loading circuit, which consumes additional current to keep the SCR working. However, pseudo loading circuit performs no function other than consuming energy, and it still consumes energy even when LED is turned off, which is unnecessary and wasteful. If the holding current of a switch can be effectively reduced, a LED illumination device would no longer need to be provided with a pseudo loading circuit. It is obvious to see that such device would be more energy-economical, and its manufacturing cost would be less, too. In addition, the trigger current required for a SCR or a TRIAC to conduct current is higher than tens of mA, and since energy-saving has become a key topic nowadays, it would be preferable to find a way to lower the required trigger current.